This invention relates to cutting tools and, more particularly, to a cutting tool for removing the exposed pintail of an aerospace blind fastener.
Blind fasteners, rivets and similar types of fastening elements commonly are used, for example, in the aerospace industry to connect overlapping structural panels forming part of an aircraft. Examples of one type of well known blind fastener are disclosed in U.S. Pat. No. 3,643,544 and, more recently, in U.S. Pat. No. 4,772,167. In general, these patented fasteners comprise an internally threaded fastener body adapted for insertion into aligned holes in two panels to be joined together, and an externally threaded stem passing in threaded engagement through the fastener body. The inserted or inner end of the stem has an enlarged head, and the outer end of the stem has a wrench engaging portion. An optional drive nut (shown in U.S. Pat. No. 4,772,167) also may be provided on the outer end of the stem for engagement with the outer surface of the fastener body. Upon turning motion of the stem relative to the fastener body, the stem is moved in an axial outward direction through the fastener body. This axial outward movement causes a deformable sleeve on the stem between the stem head and the inner end of the fastener body to deform around the fastener body until it reaches a fully set condition against the inner panel, as is known in the art.
In most cases, the fastener stem also is provided with a localized weakened region or breakgroove adapted to shear the stem along the breakgroove at a predetermined torque, after the deformable sleeve reaches its fully set condition. Ideally, the breakgroove is located axially along the stem such that the stem breaks off in substantially flush relation to the outer end of the fastener body, i.e., the fastener body head. Thus, if the fastener body head is received in a flush, countersunk relation to the surface of the outer panel, the portion of the stem remaining with the set fastener, ideally, also will be flush with the surface of the outer panel. In actual practice, however, the stem may break off approximately one-eight of an inch (i.e., 0.125 inches) above or below the outer surface of the fastener body head, an accepted industry tolerance. If an aerodynamic surface is desired, it becomes necessary to remove any exposed or protruding outer portion of any stem, this protruding portion being commonly referred to as a "pintail". According to present aerospace industry standards, the pintail may not protrude from the outer surface of the fastener body head by more than 0.006-0.008 inches. If it does, then it must be milled down or shaved to an acceptable level. Otherwise, the exposed pintails, which could number in the thousands per aircraft, would create too much turbulence and drag and adversely affect the aircraft's performance.
Over the years, various tools have been designed and employed to remove fastener pintails to achieve a flush aerodynamic panel surface. One such tool comprises a hand-held tool with a cylindrical cutter, usually made of carbide, positioned at the end of the tool. The cutter has helical cutting grooves or flutes on the outer circumferential surface of the cutter. The tool rotates the cutter in two rotational directions at the same time, i.e., around the cylindrical axis of the cutter and around an axis that is transverse or perpendicular to the cylindrical axis. This dual rotation of the tool cutter is designed to enable the operator to manually position the end of the tool over the pintail so that the rotating cutter can shave off the pintail without leaving any high spots or so-called "dead center points".
While the tool described above has been used for years for its intended purpose of removing pintails of set fasteners, there are several recognized disadvantages and drawbacks resulting from its use. For example, from the operator's standpoint, the tool is relatively heavy (weighing in some instances as much as 5-1/2 pounds), and it is cumbersome to use. The tool also tends to shake and vibrate during use due to the fluted/helical nature of the cutting grooves of the cylindrical cutter, which makes the tool prone to "dancing" on the pintail during cutting. Another operator drawback is that it usually takes about one minute to remove each pintail, depending on the height and diameter of the pintail, and the operator must apply significant force during the entire time to prevent such dancing. As a result, many operators have suffered hand and wrist injuries requiring medical treatment necessitating absence from work.
The tool discussed above also has several disadvantages from an economic standpoint. Perhaps the most significant drawback is tool maintenance. For example, the cylindrical cutter of the tool can shave off anywhere between 300-1,000 pintails, depending on the hardness of the material comprising the pintail. In a typical high volume aerospace assembly operation, it would not be unusual to shave off 1,000 pintails per tool per day. Thus, it may be necessary in the worst case to change the tool's cutter up to three times per day. Since it generally takes about 20-30 minutes to change a cutter, significant time is consumed, and down time will result unless a replacement tool is available. Significant expense also is involved, since each cutter presently costs about $300 (and each tool presently costs about $3,000). If many tools are used, the cost is multiplied even further. Yet another disadvantage is the marring and gouging of the panel surface that occurs if the cutter dances completely off the pintail during cutting. Not only is the damage unsightly, but costly repair of the surface often is necessary, especially if the damage occurs on a wing or tail section of the aircraft. While tool stabilizers have been developed to attempt to inhibit the undesirable dancing of the tool, they are relatively bulky and add further weight to the tool. Moreover, stabilizers may not be used in tight or difficult-to-access areas, since they are relatively large.
There also presently is no effective means for recovering the fragments of the pintail that are removed by known tools. This results in a messy work area and requires frequent clean up. More significant, however, is the fact that any metal scrap or debris left inside an airframe structure after it is closed up (i.e., fully assembled) can cause severe damage. Also, debris left on the surface of the wing or tail sections of the aircraft can be stepped on while working in this area and cause scratches and other damage to these skin surfaces.
Accordingly, there has existed a definite need for an effective and economical tool adapted to quickly remove the exposed pintail of a fastener without vibration. There further has existed a definite need for such a tool which also recovers the pintail and related debris resulting from the pintail cutting process. The present invention satisfies these needs and provides further related advantages.